For a motor drive unit of the numerical-control machine tool, the press machine, or the like, a system (a peak cut system) that supplies electric power temporarily required at the time of acceleration or deceleration from an electrical storage device to reduce a power supply capacity or to save contract electric power is proposed. Concerning such a system, for example, Patent Literature 1 discloses the following technique.
That is, a motor drive unit having a converter that receives an input AC voltage and performs AC-DC power conversion, and an inverter that receives DC power and performs DC-AC power conversion includes a charge/discharge control circuit and a capacitor that are parallelly connected to a link portion between the converter and the inverter, and charges or discharges energy stored in the capacitor with the charge/discharge control circuit at an arbitrary timing.
According to the technique described in Patent Literature 1, energy can be supplied from the electrical storage device in the second half of acceleration of a motor when more energy than electric power supplied from the converter during motor acceleration is required, and therefore energy supply can be achieved to suppress a peak in an input current from a power supply to the motor.